2.2 Reference Frames

Question 1

ECI

Answer 1

Earth Centered Inertial. Used for trajectory calculations of earth centered objects, non-rotating. (on earth looking up)
Primary direction: Vernal Equinox (I), 90 degrees from I along the equatorial plane, and K axis.

Question 2

ECEF

Answer 2

Earth Centered Earth Focused. Used for ground tracks and earth focused satellite effects (rotating with earth/ from the satellite looking down to earth).
Primary direction: 0 Long, 0 lat, 90 degrees from (I) along the equatorial plane, and earth’s rotational axis.

Question 3

Perifocal Frame

Answer 3

Conversion between COEs and state vectors.

Question 4

RIC

Answer 4

Radial-In track-Cross track frame. Used for relative motion.
C pointing up away from earth (angular momentum); Radial vector (pointing straight away from earth; In track (align with velocity vector).

Question 5

Topocentric Horizon SEZ

Answer 5

Used by observers on Earth’s surface.

Question 6

Sidereal Time

Answer 6

Time it takes earth to rotate exactly 360 in respect to the stars; 23hr, 56m, 4.09s, Mean solar day, on the other hand, refers to the time it takes for a specific place on earth to face the sun again.